This invention relates to vehicles which have a load bed which can be elevated at the back end thereof to align the load bed with a loading dock.
U.S. Pat. No. 4,568,094 and Re. 32,736 discloses an alignment system for vehicle load bed in which hydraulic jacks are provided for raising the back end of the load bed to achieve alignment with a loading dock. In this structure, the rear wheels of the vehicle are mounted on a support frame which is pivotally mounted on the body of the vehicle. Hydraulic jacks can be extended to raise the back end of the vehicle with respect to the frame of the wheel set. The hydraulic jacks also serve to retain the back end of the vehicle in the raised position.
Hydraulic jacking mechanisms by their nature tend to be very slow to operate. Generally, when high pressure systems of the type required in order to raise and lower the back end of a truck are supplied with hydraulic fluid, the supply is provided in a series of short injections; and as a result a considerable time is required in order to extend the hydraulic rams to a sufficient extent to raise the back end of a truck by 6 to 8 inches.
When a load is transferred from a loading dock into the back end of a van, it is common to use a fork lift truck in order to move the load items to and fro. Hydraulic rams and Jacks rely upon fluid type seals in order to remain in an extended position. Failure of the seals can result in a Ices of pressure in the hydraulic jacks and if such a failure occurs in the mechanism of Lovell, it can be extremely hazardous to drive a fork lift truck on to the elevated back end of the load bed. A failure is likely to occur in only one of the hydraulic rams and there may be sufficient power in the other ram to raise the load bed with the result that the failure would not be immediately obvious. If, however, a load is transferred On to the load bed, the load is likely to cause the load bed to tilt toward the side which is supported by the ram which has failed and this can destabilize the vehicle and the fork lift truck used for transporting the load on to the vehicle and can be very hazardous to the operator.